Dignity-wise, this is not my finest hour. I'm standing in a biomechanics lab at the University of Massachusetts Amherst while scientists attach all manner of probes and wires and monitoring devices to the lower half of my body. The electrodes are cold, and I'm not wearing pants.

Okay, technically, I do have a pair of men's bike shorts on, which were loaned to me by the institution when I turned up wearing jeans: They're tiny and tight, and when I look down at my thighs I see crude sausages, dappled ever so attractively with cadaver-blue goose bumps. Thankfully, this isn't a sexy-legs competition (though the ability to enter one might be a tangential goal)—it's an attempt to separate measurable physical fact from sales-jargon fiction: A slew of new souped-up fitness shoes, from Skechers Shape-ups to MBT shoes to Reebok EasyTones, claim to help tone muscles. Some even say that wearers can expect reduced cellulite, better circulation, relief from neck tension, and improved posture. Does this really mean that if I take a walk in them, a skinnier, more svelte me will arrive at my destination?

For today's test, I'm shod in FitFlop Sandals, arguably the most fashionable of the flab-fighting shoe brigade (they were developed in 2007 by Bliss Spa founder Marcia Kilgore in collaboration with British biomechanists David Cook, PhD, and Darren James, and have since sold more than 4 million pairs). My task is to traipse back and forth across a metal plate that records the force of each footfall. This isn't easy when trussed, Frankenstein-style, in a tangle of wires, but every element is key: While the gel insert that's stuffed into my shoe like a high-tech odor eater gauges pressure, the electrodes (brrr!) measure muscle activity, and a collection of reflective markers—attached at patella, ankle, and hip with duct tape—relay signals back to the technician's computer, generating an eerie animated image of my skeleton from the waist down, striding to and fro across the screen as if it's looking for something (like its top half). This is the same motion-capture technology employed by video game designers to create Hobbit armies and the like, and I keep suppressing a desire to scamper and swing an imaginary sword.

The data is impressive: The FitFlop's cushioning footbed significantly reduces the level of ground reaction force to my joints (the whack-back effect from every step that can ultimately damage the knees, hips, and ankles in other shoes) compared to when I perform the same actions in a pair of regular flip-flops, and the muscles in my hamstrings, thighs, and calves show increased—and prolonged—muscle engagement. "A micro-wobbleboard embedded in the FitFlop sole slightly destabilizes the body so that the muscles have to work harder to push off the ground," says Richard Jones, senior lecturer in clinical biomechanics at the University of Salford, UK, who has done extensive independent research on the shoes. Over time, the destabilization will have a toning effect on the leg.

More persuasive, though, is a comment made by another ELLE editor when I return to the office from Amherst: "I recently went to Malibu Country Mart, where you see people like Cindy Crawford and Pamela Anderson hanging out," she says, "and pretty much everyone with an awesome ass was wearing FitFlops." Impactful words. Who wouldn't want that descriptive on their list of primary characteristics? Personally, I'd be delighted to find it on my epitaph: "Here lies April Long. Awesome ass." So why am I still reluctant to wear any of these new good-for-you shoes around town? Why does the probability that they can give me a better body strike me as bad news? Because I, like many women I know, am a dyed-in-the-wool, I-don't-care-if-I-break-my-ankle high-heel devotee. Let's face it, a shoe's attractiveness invariably declines in inverse proportion to its degree of comfort: If you're slipping on a pair of Shape-ups, you've got to be willing to make a major aesthetic sacrifice.

Remember when Victoria Beckham said that she refused to go to the gym because it would require her to wear flats? That might be the one thing she and I will ever have in common. I've been wearing heels every day for at least 15 years. I love them for their elegant beauty as much as for the way they make me feel beautiful and elegant. I clap them onto my feet before I leave the house every morning, and there they stay, even on my four-mile-round-trip walk to work. I'm not going to pretend they're comfortable—I sometimes feel like I'm standing on bloody stumps, and my feet are constantly marred by stiletto stigmata: blisters, abrasions, and lingering indentations from buckles, straps, and spikes. Like most high-shoe junkies, my Achilles tendon has shortened, causing an uncomfortable straining sensation in my heel when barefoot.

The hazards of heels are legion—they put crushing pressure on the vertebrae of the lower back by forcing your derriere outward and plunging your upper body forward; they can aggregate a list of horrors including hammertoes, bunions, neuromas, and something called Haglund's Deformity, otherwise known as "pump bump." And yet, since they first became à la mode in the sixteenth-century French court, women have suffered for them—now, perhaps, more than ever. In the post–Sex and the City years, the little spikes on which we're balancing our bodies have gotten progressively taller and thinner, to the point where many of us are tottering around like newborn giraffes. Our Choos have begun to resemble chopines, the wooden platforms worn in Renaissance Italy to elevate feet out of medieval muck that had fashionable women of the day needing to use walking canes (or the shoulders of servants) to steady themselves. No wonder so many gyms now offer classes—such as New York Sports Clubs' Catwalk Confidence, created by podiatrist-in-residence Emily Splichal—that aim to strengthen the muscles that can prevent us from toppling off our shoes.

"I've seen women who have been regularly wearing five- and six-inch heels," says New York City podiatrist Suzanne Levine. "That kind of excessive height is going to guarantee back, neck, and hip problems—not to mention sprained ankles." Yet for those unwilling to trade in Manolos for EasyTones, she offers some encouragement: "A low heel—preferably below 2.5 inches—is actually far better than a ballet flat or a regular flip-flop. Walking around without any arch support at all is terrible for the spine." Furthermore, she says, it's no myth that sky-high slingbacks can boost your backside: "When you're wearing heels, your glutes have to tense up with every step you take in order to keep you stable, which will have a toning effect. I can also tell what type of shoes a person wears by looking at her calf muscles—they're much more defined in those who favor heels." Even better news? A 2008 study led by Maria Angela Cerruto, MD, a urologist at the University of Verona, Italy, found that the sustained tiptoe stance necessitated by stilettos might strengthen pelvic floor muscles in a similar way to Kegel exercises (decisive proof that those fuck-me heels really are good for your sex life).

Does this mean I can dismiss the FitFlop-is-better-for-you flap and trot happily into a tall, taut future? Not so fast, Levine cautions. While she believes that many of the claims (cellulite reduction; the notion that they can replace the gym) made by like-minded workout-while-you-walk shoe manufacturers are "nonsense," they do provide a safe, and necessary, comedown for body and sole. "If you're walking for longer distances, a FitFlop-type shoe is going to work muscles while also supporting and protecting the foot—although I have seen some widening in the arch of people who wear them all the time because the instability of the sole causes feet to pronate outward," she says. "The key is to not wear anything every single day." High-heel abuse can also be somewhat mitigated by doing daily stretching exercises: "Pick up pencils with your toes, roll your foot around on a tennis ball, and flex your ankle like you're pressing a gas pedal," she suggests.

A few weeks after my lab-rat experience at Amherst, I go for a walk through Central Park with Jay Cardiello, a FitFlop-endorsing strength and conditioning coach. (He's also 50 Cent's personal trainer, and I realize later that I've forgotten to ask him the million-dollar question: "Does Fitty Flop?") When I admit to him that today is the first time I've walked any considerable distance wearing the shoes, he fixes me with a piercing stare. "A lot of times we don't realize the damage we're doing today, but we'll feel it tomorrow," he says. "See how she's walking on the outsides of her feet?" he says, pointing at a flip-flopper just ahead of us on the path. "Those shoes are doing nothing to correct that—in fact, they're worsening it—and in a few years, she's going to have knee damage." He shakes his head. "FitFlops aren't just for people who want their bodies to look better," he says. "They're also for people like you who spend a lot of time sitting at their desks, gradually losing the strength in their lower lumbar area."

Yikes.

As he talks, I feel my feet sinking bliss-fully into the cradling comfort of the FitFlop insole, and I begin to wonder, What's my problem with flat shoes, anyway? Who on earth am I trying to impress by wearing three-inch mules to walk my dog? Really, what's important here? After all, no matter how beautiful a shoe might be, if the foot you're cramming into it has hammertoes, it's not going to be so pretty. And if donning a good-for-you shoe from time to time is going to increase the likelihood that I'll be able to stride into my dotage in Louboutins rather than Aerosoles, then I'm sold. When I wave goodbye to Cardiello, I keep the FitFlops on. And the next morning, I walk to work in them, my beloved heels tucked securely in my bag. If only we could talk Mr. Louboutin into fitting a FitFlop into one of his designs, all my problems would be solved.